1. Field of the Invention
The present invention relates to computer implemented transaction processing systems. More particularly, it relates to distributed transaction processing systems and still more particularly to object oriented distributed transaction processing systems incorporating transaction monitors.
2. Background and Related Art
Computer implemented transaction processing systems are used for critical business tasks in a number of industries. A transaction defines a single unit of work that must either be fully completed or fully purged without action. For example, in a bank automated teller machine (ATM) from which a customer seeks to withdraw money, the actions of issuing the money, reducing the balance of money on hand in the machine and reducing the customer's bank balance must all occur or none of them must occur. Failure of one of the subordinate actions would lead to inconsistency between the records and actual occurrences.
Distributed transaction processing involves a transaction that affects resources at more than one physical or logical location. In the above example, an ATM transaction affects resources managed at the local ATM device as well as bank balances managed by a bank's main computer. A distributed transaction may not be physically distributed but may involve cooperating tasks that must be completed in synchrony for successful transaction completion.
The X/Open Company Limited (X/Open is a trademark of X/Open Company Ltd.) has promulgated a guide that describes one model for implementing distributed transaction processing. The X/Open Guide, Distributed Transaction Processing Reference Model, October 1991, discusses the components of a distributed transaction system and the interrelationships between them. The X/Open Distributed Transaction Processing Model (the DTP Model) describes three main components: an Application Program (AP), a Transaction Manager (TM), and one or more Resource Managers (RMs). The Application Program uses and modifies the resources controlled by one or more of the Resource Managers. The Transaction Manager is responsible for global transactions and coordinates the decision whether to commit or roll-back the actions taken by the Resource Managers. (Commit causes the resources to be updated while roll-back causes all work to be discarded returning the resources to the state they were in upon transaction initiation.) The Resource Managers manage specific resources. Resource managers may include a database management system (DBMS), a file system, or similar resource.
Object oriented programming systems are designed to increase the efficiency of program development by enabling object reuse and simplifying system maintenance through clear separation of function.
Each object in an object oriented system encapsulates the data for that object and the procedures or methods for operating on that data. Encapsulation means that the data for an object can be manipulated only by that object using the defined methods.
Object oriented systems also implement object inheritance. Inheritance allows a more specific object to be derived from a general object. The more specific object can "inherit" all of the data and methods of the parent object, but can override selected data and methods and add others to implement its unique function.
The application of object oriented techniques to transaction processing systems raises many new issues but offers opportunities to increase system efficiency through the use of object oriented principles. The Object Management Group, Inc. (OMG) has established standards for interoperable object oriented systems. The overall architecture defined by OMG is the Object Management Architecture (OMA). A central component of OMA is the Object Request Broker that enables objects to send messages to other objects. The Common Object Request Broker Architecture (CORBA) defines the interactions between objects, and in particular, between distributed objects in different computer systems. The ORB provides location transparency and hides the details of communications between objects. CORBA is specified in the OMG publication entitled, The Common Object Request Broker: Architecture and Specification, March 1992.
OMG has accepted a specification to standardize transaction processing in object oriented systems. This specification, entitled the Object Transaction Service (OTS) Specification, sets forth the requirements for object services necessary to implement a transaction processing system. The OTS specification uses many of the unique capabilities of object oriented systems. The OTS model, however, is designed to allow object oriented systems to operate with the X/Open DTP model and with existing procedural transaction processing systems.
Efficient transaction processing requires that the resources committed to transaction processing be efficiently scheduled. A particular computer system has constraints on processor throughput, memory allocation and input/output capacity. Transaction throughput can be increased by improving the efficiency of transaction processing scheduling. Prior art procedural transaction processing systems have implemented transaction processing scheduling in the form of a transaction monitor or TP Monitor.
Existing transaction monitors, however, are written to support a particular transaction processing system. Transaction monitors exist in the IBM CICS and IMS transaction processing systems and in the Tandem Transaction Management Facility (TMF) system. No object oriented transaction processing system currently implements a transaction monitor.
The technical problem therefore exists to implement a transaction scheduling system for an object oriented transaction processing system. A second technical problem is to develop an overall transaction processing system that can interchangeably use different transaction monitors depending on the particular application requirements. Another technical need is to be able to tune transaction processing by modification of the object activation scheduling process.